The Lizard casters in Temple of Cazic Thule (justicar/judicator/lifedrinker/lifestealer etc) have a fairly good drop rate on this. I camped the throne room area for the clicky levitate shield for maybe 7 to 8 hours , and managed to gather 60-70 powders as a lvl 60 cleric duoing with a 58 SK and 2 mercs , so we were killing at a slow rate (they have a nice amount of hp though...).

Can add a Mangled Clairvoyant to the Greig's End list of mobs. Seems mobs other than those on the above list drop Binding Powder with more frequency than those on the list. Just an observance after hundreds if not thousands of kills in this zone.

I never hunted in any of these zones for exp since I've been back but I managed to scrounge up 43 of the binding powders. My only guess is Bastion of Thunder but not being a hotzone anymore is kind of useless for farming, they are still pretty tough...